Mechanisms to Adjust Urine Concentration - McCormick

Question 1

Na reabsorption in PT

Answer 1

50-55%
Na/H exchanger
Cotransport with glucose, AA, phosphate

Question 2

Na reabsorption in TAL

Answer 2

35-40%
Na/K/2Cl
Impermeable to water

Question 3

Na reabsorption in DCT

Answer 3

5-8%

Na/Cl cotransporter

Question 4

Na reabsorption in Late DCT/CD

Answer 4

2-3%

Luminal Na+ membrane channels

Question 5

Chloride reabsorption

Answer 5

Always linked either directly or indirectly to Na reabsorpton

Question 6

Descending loop of Henle

Answer 6

Freely permeable to water

Impermeable to Na+, Cl-

Question 7

Transport in first half of DCT

Answer 7

Tubular urine:
Na/Cl
K/Cl
Blood side:
Na/K
K leak
Cl leak

Question 8

What is the major site of physiological control of salt and water balance?

Answer 8

Late DCT/CD

Question 9

What hormones control salt and water balance?

Answer 9

Aldosterone - Na reabsorption, K and H secretion
ANP - Inhibits Na reabsorption
ADV - water reabsorption

Question 10

What is the driving force for K and H secretion by the principal cells?

Answer 10

The large transepithelial potential

-50 mV, lumen negative

Question 11

How does Aldosterone increase Na reabsorption in principal cells

Answer 11

Incorporation of Na channels in luminal membrane

Incorporation of Na/K ATPase in basolateral membrane

Question 12

How does ADH increase H2O permeability in Late DCT/CD?

Answer 12

Via V2 receptors and insertion of aquaporin channels

Question 13

Countercurrent multiplier mechanism

Answer 13

Concentrates solute in medullary interstitium

High solute conc enables kidney to excrete high conc urine

Question 14

How does urea get concentrated in inner medulla?

Answer 14

ADH promotes reabsorption form inner medullary CD

Question 15

Describe urine in antidiuresis

Answer 15

Low volume, high urine concentration

Question 16

Describe urine in diuresis

Answer 16

High volume of dilute urine is excreted

Question 17

Talk to me about obligatory urine volume

Answer 17

The body generates 600 mOsm waste/day
Can concentrate to 1200 mOsm
SO…. minimum to remove waste is 0.5 L/day

Question 18

Osmolar clearance

Answer 18

Uosm x V/Posm

Question 19

Free water clearance

Answer 19

Excretion of water in excess of amount needed to excrete isosmotic urine

Question 20

If Uosm < Posm is positive

Answer 20

Pure water is cleared from body

Question 21

If Uosm > Posm is negative

Answer 21

Pure water is retained

Question 22

Fractional excretion

Answer 22

The fraction (percentage) of the filtered load of a substance that is secreted in urine

UP/PU
(Na is first, cr second)

Question 23

Fractional excretion < 1%

Answer 23

Pre renal and AGN

Na avidly reabsorbed

Question 24

Fractional excretion > 2%

Answer 24

ATN, Renal